If you’ve been on social media this week, you might have noticed Californians going crazy over the sudden appearance of millions of butterflies, flying north en masse through the state. It’s pretty much the exact joyful display of nature that the world needs right now.

But it’s also a beautiful and rare sight in a world where insects are disappearing more rapidly than ever before. Experts are saying there hasn’t been this kind of butterfly migration through the state since 2005.

So what’s going on?

1) Walking the dogs this a.m. I found myself in the midst of the Butterfly migration. My first experience with this phenomenon. I’d imagined it to be a casual, drifting multitude, like a confetti cloud. Not at all. These “Painted Ladies” were headed north with speed & purpose– pic.twitter.com/J0IazDDjVB

Every winter, these incredible, brightly coloured butterflies mature in the Californian and Mexican deserts before heading north altogether for the summer – travelling at a breakneck 25 miles per hour (40 kilometres per hour) and barely stopping.

Southern California friends: I just sat on the beach in the South Bay for two hours while 1,000s of butterflies flew around and past me. What kind are they? What is happening? #butterfliespic.twitter.com/n1IrEaBy0D

While we still don’t know a whole lot about the life cycle of the butterflies, we know they lay their eggs on plants and also feed on those plants after they’re born – so the more flowers there are, the more butterflies we get.

Fun fact: Over in Europe the migration is even more epic, with painted ladies completing the farthest known butterfly migration in the world, flying 7,500 miles or 12,000 kilometres and crossing the Sahara.

Unfortunately, we might not see this type of butterfly explosion in future years.

While scientists have been concerned about the decline of flying insects for years, a study earlier this year showed just how dire the situation has become.

“A newly published review of 73 reports on insect decline around the world has found that over 40 percent of insect species are threatened with extinction. For some comparison, that rate of local species extinction is eight times faster than we’re seeing in vertebrates such as mammals, birds, and reptiles.”

Scientists still aren’t quite sure exactly what is driving these insect deaths, with pesticides, climate change, and habitat loss all implicated.

Let’s hope this beautiful experience might make more people care about the plight of these incredible insects, and what we can do to protect them while they’re still around.